Initial commit: RegionIO Minecraft server core (26.1.2/protocol 775)

Vanilla-faithful overworld generator (final_density + multi-noise biomes),
full connection lifecycle (status/login/configuration/play), chunk streaming,
creative block editing, and the protocol/nbt/registry infrastructure.

internal/worldgen/blendedcompute_test.go

@@ -0,0 +1,16 @@
+package worldgen
+import ("math";"testing")
+func TestBlendedCompute(t *testing.T){
+	bn:=NewBlendedNoise(NewXoroshiro(42),0.25,0.125,80.0,160.0,8.0)
+	cases:=[]struct{x,y,z float64;want float64}{
+		{0,64,0,-0.012282880040235755},
+		{100,40,-200,0.007126388725845459},
+		{1234,80,-5678,-0.13408933571823986},
+		{-37,128,99,-0.0932958728408956},
+		{8,200,8,0.0075622598474688885},
+	}
+	for _,c:=range cases{
+		got:=bn.Compute(FunctionContext{X:c.x,Y:c.y,Z:c.z})
+		if math.Abs(got-c.want)>1e-12 { t.Fatalf("bn(%v,%v,%v)=%v want %v (diff %v)",c.x,c.y,c.z,got,c.want,got-c.want) }
+	}
+}